Hydraena arcta, Published, 2007

PERKINS, PHILIP D., 2007, A revision of the Australian species of the water beetle genus Hydraena Kugelann (Coleoptera: Hydraenidae), Zootaxa 1489 (1), pp. 1-207 : 48-49

Hydraena arcta new species

(Figs. 75, 78, 240)

Type Material. Holotype (male): Western Australia, Synnot Ck., CALM Site 25/1 [Western Australian Department of Conservation and Land Management], 16° 31' S, 125° 16' E, at light, closed forest margin, 17– 20 June 1988, T. A. Weir. Deposited in the ANIC . Paratypes: Same data except at light, open forest (7 ANIC) .

Differential Diagnosis. Recognized from all species, except H. weiri and H. tenuisella , by the very flat, narrow, parallel-side form (Figs. 67, 74, 75). H. arcta is smaller than both H. weiri and H. tenuisella (ca. 1.13, 1.25, 1.39 mm respectively), and the microreticulation of the frons and clypeus is stronger; however, these species are otherwise very similar in dorsal sculpture and plaque proportions; reliably distinguishing among the three species will require examination of the aedeagi (Figs. 78–80).

Description. Size (length/width, mm) holotype: body (length to elytral apices) 1.13/0.42; head 0.16/ 0.28; pronotum 0.29/0.35, PA 0.29, PB 0.31; elytra 0.67/0.42. Head dark brown to piceous; pronotum brown, anterior angles slightly lighter; elytra brown; legs and palpi light brown to testaceous, tip of last palpomere not darker.

Frons punctures ca. 1xef; interstices weakly shining on middle of disc, microreticulate and dull anteriorly, 2–3xpd. Clypeus microreticulate. Mentum weakly shining, very finely sparsely punctate; postmentum microreticulate. Genae weakly raised, lacking posterior ridge. Pronotum finely sparsely punctate; punctures on disc ca. 1xpd those of frons, interstices strongly shining, 2–5xpd, largest on disc; PF1 and PF4 absent; PF2 very shallow, almost absent; PF3 very shallow, broad.

Elytral punctures ca. 1xpd of smallest pronotal punctures. Intervals not raised, shining, width about 2– 3xpd, as are interstices between punctures of a row. Elytra parallel-sided or nearly so. Apices in dorsal aspect truncate, in posterior aspect margins form shallow angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 2/2/7/2. P1 laminate; median carina weakly angulate in profile. P2 l/w ca. 5/2, sides parallel or weakly diverging, apex blunt. Plaques large, slightly raised, located in posterior 3/5 of metaventrite on sides of shallow median depression; plaques straight, parallel or nearly so, very weakly tapering anteriorly. AIS flat, width at arcuate posterior margin ca. 1.5x P2. Legs simple, except metatibia (male) with indistinct row of short, sparse hair-like setae over distal 1/2 of inner surface. Last tergite cap-like, with small apicomedian notch.

Aedeagus (Fig. 78) main-piece enlarged distally, with two or three rounded lobes and one sharply pointed process; distal piece with a large spiculate lobe and two narrow processes, process that terminates in gonopore-bearing flagellum widened before flagellum; left paramere very narrow, shorter than right, with about seven setae on ventral surface apically; right paramere inserting above level of left, enlarged basally, arcuate, sharply pointed, with about five long setae on ventral surface near midlength. Female last tergite with very minute apicomedian incision, setae slender, tapering.

Etymology. Named in reference to the very thin body form.

Distribution. Currently known only from the type locality in the Synnot Range, northeastern Western Australia (Fig. 240).